[c-nsp] Pseudowire VC Types on Cisco

[James Bensley]

Hi Waris and all,

Thanks for your response although this has left me with some
confusion. Are you able to clarify for me the following behaviour,
based on what you have said?

Since VC type 5 is default for EVCs, the following configuration
allows me to pass untagged frames over a pseudowire:

interface GigabitEthernet0/1
 switchport trunk allowed vlan none
 switchport mode trunk
 service instance 11 ethernet
  encapsulation untagged
  xconnect 10.0.0.2 123 encapsulation mpls


This configuration allows me to pass tagged frames over a pseudowire:

 service instance 11 ethernet
  encapsulation dot1q 11
  xconnect 10.0.0.2 123 encapsulation mpls


In both cases the PEs show the pseudowire as VC type 5 "Ethernet", so
presumably the dot1q tags are forwarding in the 2nd EVC example
because the PEs are signalling the local AC encapsulation type to each
other (I haven't got wireshark/tcpdump here to check) as one would
expect, so VC type 5 circuits can carry tagged or untagged as long as
it's signalled when the pseudowire is established, is this
understanding correct?

When making a port based pseudowire, this configuration allows me send
untagged frames but not tagged frames, and the pseudowire is
established as VC type 5:

interface GigabitEthernet0/1
 description ME3600-Gi0/3
 no switchport
 no ip address
 xconnect 10.0.0.2 123 encapsulation mpls

To send dot1q tagged frames on a port based pseudowire I must use
"interworking vlan" at each PE which then forces the pseudowire to VC
type 4.

For port based pseudowires are the PEs signalling the local AC
encapsulation as if it were configured as "encapsulation untagged"? I
was hoping they would signal the AC type as the equivalent of
"encapsulation default" so it would carry untagged, dot1q and qinq
frames blindly. Can anyone confirm the behaviour here?

I have noticed when trying to ping over a port based pseudowire with
"interworking vlan" sending untagged traffic into the ingress PE, at
the egress PE a tagged frame is coming out and into the layer 2
switch. The layer 2 switch connected to the egress PE is showing a
corresponding increase in received dot1q tagged frames with "show int
gi0/4 controller  | i Dot".

So I assume here in VC type 4 the ingress PE is pre-pending a dummy
VLAN tag but the egress PE isn't striping it? Is that correct?

Cheers,
James.